The invention relates to polymerizable compositions containing high index of refraction monomers, and polymeric materials prepared therefrom.
Optical materials and optical products can be prepared from high index of refraction materials such as polymerizable, high index of refraction monomers and curable compositions containing such high index of refraction monomers. An example of useful high index of refraction monomers are bromine-substituted aromatic (meth)acrylate monomers. See for example U.S. Pat. No. 4,578,445. Such monomers can typically be relatively high melting materials that exist in the form of a solid at or around room temperature, and often have melting points significantly above room temperature. Because these monomers exist as solids at room temperature, curable compositions containing these monomers must either be dissolved into solution, or heated to their melting points (above room temperature) to be processed and formed into a high index of refraction optical product.
The need to heat high index of refraction materials during processing adds significant complication and expense to the processing of the material into an optical product. Processing lines must be heated, which can require large amounts of energy, can sometimes rupture tubing connections, and can even cause the evolution of volatile organic compounds, thereby potentially creating a hazardous work environment. If complete and uniform heating is not consistently maintained, the monomer can crystallize within the curable composition during processing, resulting in the production of non-uniform and unusable product, and resulting in high amounts of waste product. And, maintaining the polymerizable composition at an appropriate processing temperature can potentially cause prepolymerization of the monomeric composition. Of course, all of these added process requirements and negative consequences increase the cost of producing high index of refraction products from curable compositions that exist as solids at room temperature.
It would be advantageous to identify a polymerizable composition useful to produce optical materials and optical products having a relatively high index of refraction, and a relatively low melting point, e.g., a polymerizable composition that can be processed as a liquid at temperatures equal to or near normal room temperature.
In a general sense, the present invention provides polymerizable compositions having a high index of refraction, and preferably, high index of refraction polymerizable compositions that can be processed at temperatures at or near room temperature (e.g., in the range from about 20 to 25xc2x0 C.) to produce a polymer or polymeric material. The polymerizable composition contains brominated, high index of refraction monomers. The monomer and the composition can each have relatively low melting points, and desirable optical properties.
Monomers useful in the composition include alkyl-substituted brominated phenolic (meth)acrylate monomers that have relatively high indexes of refraction, and that can preferably be liquid at temperatures between near room temperature and 60xc2x0 C. Even those brominated monomers that are solids in this temperature range can be desired because these can often be easily dissolved in liquid polymerizable compositions of the present invention without significantly raising the melting point of the polymerizable composition. Thus, a polymerizable composition containing these monomers can preferably have a relatively low melting point, and can more preferably exist in the form of a liquid at temperatures at or around room temperature, thereby reducing or eliminating the need to heat these compositions during processing. The invention thereby eliminates expense and complication otherwise associated with heating a polymerizable composition to prepare high index of refraction polymeric materials. By xe2x80x9cprocessing,xe2x80x9d it is meant that the monomer or polymerizable composition can be blended, pumped, or otherwise handled prior to polymerization and manufacturing to produce a polymer or optical product.
An aspect of the invention relates to a polymerizable composition containing an alkyl-substituted brominated aromatic ester (meth)acrylate monomer, the brominated monomer preferably having an index of refraction of at least 1.50. The polymerizable composition further contains one or more comonomer or comonomers, including at least one high index of refraction comonomer.
Yet another aspect of the invention relates to polymer or polymeric material comprising monomeric units derived from the above-described polymerizable composition. Specifically, the invention relates to a polymer or polymeric material derived from ingredients including an alkyl-substituted brominated aromatic ester (meth)acrylate monomer, the brominated monomer preferably having an index of refraction of at least 1.50, and one or more comonomer or comonomers, including at least one high index of refraction comonomer.
As used within the present description.
xe2x80x9cMonomerxe2x80x9d refers to a monomer on an individual scale, and also refers collectively to a composition of such monomers on a macroscopic scale such that the composition can be described as having a physical state of matter (e.g., liquid, solid, etc.) and physical properties (e.g., melting point, viscosity, glass transition temperature (of a polymeric form of the monomer), or refractive index).
xe2x80x9cMelting point,xe2x80x9d as used with respect to the monomer, refers to the temperature at which the monomer passes from a solid to a liquid state, as measured at atmospheric pressure. Melting point can be measured, for example, using a Thomas-Hoover Melting Point Apparatus, from Thomas Scientific of Swedesboro N.J.
xe2x80x9cIndex of refraction,xe2x80x9d or xe2x80x9crefractive index,xe2x80x9d refers to the absolute refractive index of a material (e.g., a monomer) which is understood to be the ratio of the speed of electromagnetic radiation in free space to the speed of the radiation in that material, with the radiation being sodium yellow light at a wavelength of about 583.9 nm. Index of refraction can be measured using an Abbe Refractometer.
(Meth)acrylate refers to both acrylate and methacrylate compounds.
The present invention describes a polymerizable composition comprising an alkyl-substituted brominated phenolic ester (meth)acrylate monomer. As used within the present description the term xe2x80x9cpolymerizablexe2x80x9d refers to a chemical molecule such as a monomer or oligomer, etc., or a chemical composition, capable of polymerizing or copolymerizing (e.g., via unsaturated moieties) to produce a higher molecular weight material such as a polymer or polymeric material. xe2x80x9cPolymerxe2x80x9d or xe2x80x9cpolymeric materialxe2x80x9d are used interchangeably to refer to materials prepared from the reaction of one or more unsaturated materials, e.g., one or more monomer, oligomer, or polymer, prepolymer, etc., and includes, e.g., dimers, trimers, oligomers, pre-polymers, copolymers, homopolymers, etc.
The alkyl-substituted brominated aromatic ester (meth)acrylate monomer, also preferred to herein as xe2x80x9cthe Monomer,xe2x80x9d or the xe2x80x9cBrominated Monomer,xe2x80x9d preferably has physical properties that allow processing of the composition at or near room temperature to produce a high index of refraction optical product. Thus, the Brominated Monomer has a relatively high index of refraction, and preferably has a relatively low melting point.
The substituents of the aromatic portion of the Monomer can affect or substantially determine the physical properties of the Monomer, including index of refraction and melting point. These properties are believed to be affected by the chemical composition of the substituents, the size and number of such substituents, and the location of such substituents on the monomeric structure, e.g., on the aromatic portion of the Monomer. While wishing not to be bound by theory, the alkyl substituent (e.g., its size, position, and chemical composition) is believed to affect the melting point of the Monomer. Further, the position of the alkyl group on the aromatic portion of the Monomer can affect the size of the alkyl group required to provide a desired physical property such as melting point. That is, preferred alkyl groups in the para position that provide a desired melting point or index of refraction may be of a size range different from preferred alkyl groups in the meta or ortho positions that also provide the desired property. Preferably, the alkyl group has a chemical composition and position such that the Monomer has a melting point below about 60xc2x0 C., more preferably below about 35xc2x0 C. or 30xc2x0 C., even more preferably below about 25xc2x0 C., and most preferably the Monomer exists in a liquid state at about 23xc2x0 C.
A property related to melting point of the Monomer is viscosity. The Monomers of the present invention preferably are of a viscosity (at 23xc2x0 C.) that allows the Monomer or a polymerizable composition comprising the Monomer to be processed at room temperature (without heating) to produce a high index of refraction polymer or polymeric material. Although viscosities outside of these ranges can also be useful, preferred viscosities of the Monomer can be below about 10,000 cps, for example in the range from about 100 to 5000 centipoise (cps), more preferably from about 300 to 4000 cps. Viscosity can be measured by known methods, for example using a viscometer such as a Brookfield viscometer.
The chemical composition and position of the alkyl on the aromatic ring can also tend to affect the index of refraction of the Monomer. Thus, while wishing not to be bound by theory, and while observing that Monomers having relatively larger alkyl groups can be useful within the present invention, it can be said that in a very general sense larger alkyl groups can result in a lower index of refraction.
The index of refraction of the Monomer can also be affected by the presence and position of bromine on the monomer. It is generally understood that the presence of bromine increases the index of refraction of the Monomer. Bromine can be present on the monomer at any useful position and in any amount to provide a Monomer having one or more of the above-described desired physical properties. Preferably, the Brominated Monomer has bromine attached in a sufficient amount and at appropriate positions to produce a monomer having an index of refraction of at least 1.50, more preferably at least 1.55, or 1.56. This can be accomplished, for example, by having at least two bromines directly attached to the aromatic portion of the Monomer. Often, the position of the bromine can be a function of the materials and process used to prepare the Brominated Monomer (described infra). Also, the position of the bromine can depend at least in part on the position of the alkyl. If the alkyl is attached at the 4 position relative to the ester substituent, bromines are preferably at the 2 and 6 position, and, if the alkyl is at the 2 position, bromines are preferably at the 4 and 6 positions.
Examples of Brominated Monomers useful in the practice of the invention include alkyl-substituted brominated aromatic ester (meth)acrylate monomers of general formula: 
In formula 1, R can be hydrogen (xe2x80x94H) or methyl (xe2x80x94CH3), RA can be a straight or branched alkyl preferably having from 1 to 18 carbon atoms, and x can be in the range from about 1 to 4, with the combination of these variables preferably being such that the brominated monomer has an index of refraction of at least 1.50. RA can be positioned ortho, meta, or para to the ester.
A particularly preferred class of Brominated Monomer are those comprising an aromatic portion substituted with an alkyl at the position ortho to the ester substituent: 
In FIG. 2, R and x are as defined with reference to FIG. 1, and R1 is an alkyl according to RA. Preferably, R1 can be an alkyl group to provide a monomer having an index of refraction of at least 1.50, e.g., an alkyl group having from about 1 to 18 carbon atoms, more preferably from about 3 to 12 carbon atoms. Also preferably, the Monomer can have at least two bromines attached directly to the aromatic ring. In a particularly preferred embodiment of this Monomer bromines are located at the 4 and 6 positions on the aromatic ring, ortho and para to the ester substituent: 
Particular Monomers according to formula 3 include 4,6-dibromo-2-alkyl phenolic ester (meth)acrylates, wherein the alkyl (R1) has from 3 to 12 carbons, for example from 3 to 4 carbon atoms. Examples of such Monomers include the following:
4,6-dibromo-2-sec-butyl phenyl (meth)acrylate: 
xe2x80x834,6-dibromo-2-tert-butyl phenyl (meth)acrylate: 
4,6-dibromo-2-isopropyl phenyl (meth)acrylate: 
A second particularly preferred class of Brominated Monomer comprises an aromatic portion substituted with an alkyl group at the position para to the ester substituent: 
In FIG. 4, R and x are as defined with reference to FIG. 1, and R2 is an alkyl such as RA. Preferably, R2 can be an alkyl group to provide a Monomer having an index of refraction of at least 1.50, e.g., an alkyl group having from about 1 to 18 carbon atoms, more preferably from about 3 to 12 atoms. Also preferably, the Monomer can have at least two bromines attached directly to the aromatic ring. In a particularly preferred embodiment of this Monomer, bromines are located at the 2 and 6 positions on the aromatic ring, each being ortho to the ester substituent: 
One particularly preferred para-substituted alkyl group is nonyl, giving dibrominated-4-nonyl phenyl (meth)acrylate monomers, such as 2,6-dibromo-4-nonyl phenyl (meth)acrylate: 
Another particularly preferred para-substituted alkyl group is dodecyl, giving dibrominated-4-dodecyl phenyl (meth)acrylate monomers, such as 2,6-dibromo-4-dodecyl phenyl (meth)acrylate: 
The Brominated Monomers can be prepared by any method generally useful in preparing brominated phenolic compounds, and in particular alkyl-substituted brominated phenolic ester (meth)acrylates. Such methods are well known in the chemical art. By one particular method, an alkyl-substituted phenol can be brominated to produce a brominated alkylphenol. Alkylphenols are commercially available, for example, from Schenectady International, Inc., Chemical Division, Schenectady N.Y. Such alkyl-substituted phenols can be brominated by methods that are generally known in the chemical art, and are described, for example, in the Kirk-Othmer Encyclopedia of Chemical Technology, volume 4, 543 (4th ed. 1992). An example of such a process, show with respect to an ortho-substituted alkylphenol, is as follows: 
In a second step of this method, the brominated alkylphenol can be esterified to produce an alkyl-substituted brominated phenolic ester (meth)acrylate, by reaction with an appropriate acid chloride. The reaction between an alcohol and an acid chloride is well known in the chemical art, and is described, for example, in the Kirk-Othmer, Encyclopedia of Chemical Technology, volume 9, 769 (4th ed. 1992; see also U.S. Pat. No. 3,845,102). Inhibitors, such as phenothiazine or 4-methoxyphenol (MEHQ), can be used in such an amount to provide protection from pre-polymerization of the Monomer during its synthesis and storage, while not excessively influencing the subsequent polymerization. With respect to the Monomer of the present invention, the brominated alkylphenol can be reacted with (meth)acryloyl chloride as shown: 
The Brominated Monomer can be used alone or in combination with one or more comonomers or high index of refraction comonomers to prepare a polymerizable composition that can be polymerized or copolymerized to produce useful polymers or polymeric or copolymeric materials. As will be apparent in light of the various examples below, the molecular weight of a comonomer can be within a large useful range. As used within the present description the term xe2x80x9ccomonomerxe2x80x9d can refer not only to those materials generally known in the chemical art as xe2x80x9cmonomers,xe2x80x9d but also to relatively higher molecular weight materials including materials comprising polymerizable oligomers, and also relatively higher molecular weight materials such as polymerizable pre-polymers and polymerizable polymers. Preferably, a high index of refraction monomer will have an index of refraction of at least about 1.50.
The comonomer can comprise any of a number of known and useful polymerizable unsaturated moieties, e.g., vinyl, (meth)acrylate, N-vinyl, acrylic acid, methacrylic acid, allyl, acrylamide, acrylonitrile, etc. The comonomer can be mono- or multifunctional with respect to the unsaturated moiety, and where multifunctional, the unsaturated moieties need not be of identical chemistry.
One class of comonomer found to be useful in the polymerizable composition is the class of (meth)acrylate-functional monomers having an index of refraction of at least about 1.5. Such (meth)acrylate functional comonomers can have a structure within the general formula: 
In formula 8, R can be hydrogen (xe2x80x94H) or methyl (xe2x80x94CH3), y is preferably from about 1 to 6, and R3 can be of any chemical structure that allows polymerization of the comonomer via the unsaturated moiety or moieties, and preferably provides a comonomer having an index of refraction of at least 1.50. Preferably, to achieve a sufficiently high index of refraction, R3 can include one or more chemical moieties known in the optical products art as providing optical activity such as an aromatic moiety, cyclohexyl, a halogen such as chlorine, bromine, or iodine, or a sulfur containing group. Further, however, the R3 group can optionally comprise one or more other chemical moieties or structures, for example oxyalkylene, urethane, epoxy, alkyl, and/or allyl groups, etc., any of which can be straight, branched, cyclic, or unsaturated.
Examples of specific useful (meth)acrylate-functional comonomers include a number of commercially available mono-, and multi-functional (meth)acrylate monomers, including hexa-functional aromatic urethane acrylate oligomer available from UCB Radcure Inc., under the designation EB 220, and 2-phenoxyethyl acrylate, sold under the name Photomer 4035 by Henkel Corp., of Ambler Pa., among others. The above-listed (meth)acrylate-functional comonomers are not halogenated. Particularly preferred polymerizable compositions of the present invention comprise the above-identified Brominated Monomer, and further comprise comonomer comprising a halogenated (i.e., brominated, iodinated, or chlorinated) aromatic (meth)acrylate comonomer. Examples of such halogenated monomers include tribromophenoxy acrylate, tribromo phenyl acrylate, tetrabromobisphenol A diacrylate, ethoxylated tetrabromobisphenol A diacrylate, pentabromophenylacrylate, tetrabromo xylyl diacrylate, 2-(2,4,6-tribromophenyl)-1-ethanol acrylic ester, sold as BR-31 (CAS #7347-19-5) by Dai-Ichi Kogyo Seiyaka Co. of Japan, and brominated epoxy diacrylate manufactured by UCB Chemicals Corp., Radcure, in Smyrna, Georgia, under the designation RDX 51027. Some of these monomers are crystalline solids at room temperature. Especially preferred monomers are those that exist as low viscosity liquids at room temperature.
Another preferred comonomer is methyl styrene, having the formula: 
Methyl styrene exists and is useful in the polymerizable composition as any of various isomeric structures, including ortho-, meta- and para- isomers. Methyl styrene is commercially available as a mixture of one or more of these isomers. For example, methyl styrene can be used and is commercially available in ratios of 80:20, 70:30, 60:40, 55:45, and 5:90 (meta:para): 
Methyl styrene is commercially available from Monomer-Polymer and Dajac Laboratory in Feasterville, Pa. Alternatively, methyl styrene can be prepared by methods known in the chemical art; see the Encyclopedia of Polymer Science and Engineering, volume 16, p. 13, (2nd ed. 1985).
The use of methyl styrene as a high index of refraction monomer for the production of optical products is described in Assignee""s copending United States patent application entitled xe2x80x9cMethyl Styrene as a High Index of Refraction Monomer,xe2x80x9d having U.S. Pat. No. 6,107,364 filed on even date herewith, and incorporated herein by reference.
The particular comonomers included in any given polymerizable composition, their molecular weight or molecular weights, and the amounts of each, can be chosen according to factors such as the desired nature and properties of the polymerizable composition, and the desired properties of the polymer or polymeric material to be prepared therefrom (e.g., index of refraction, glass transition temperature, melting point, viscosity, etc., of the polymerizable composition or polymeric material).
The amount of the Brominated Monomer present in the polymerizable composition can be any amount that will allow the production of a polymer or polymeric material having desired optical and mechanical properties. For example, and while amounts outside of this range can also be useful, it can be preferred to use from about 5 to 50 parts by weight, more preferably from about 25 to 40 parts by weight Brominated Monomer, based on 100 parts by weight of the polymerizable composition.
The comonomer can also be present in the polymerizable composition in any useful amount. For instance, the comonomer can be present in an amount in the range from about 50 to 95 parts by weight, more preferably from about 60 to 75 parts by weight, based on 100 parts polymerizable composition.
The comonomer can comprise one or a combination of one or more comonomers or high index of refraction comonomers. For instance, the comonomer can comprise a mixture of one or more (meth)acrylate monomers (including mono-, and/or multifunctional monomers), the comonomer can comprise this type of mixture and can further comprise methyl styrene, or, the comonomer can comprise either of the above-described mixtures, and can further include an aromatic (meth)acrylate monomer (e.g., a brominated aromatic (meth)acrylate monomer). In a particularly preferred embodiment, the polymerizable composition comprises from about 25 to 40 parts by weight of the Brominated Monomer, from about 5 to 15 parts by weight methyl styrene monomer, and from about 45 to 70 parts by weight of one or a combination of (meth)acrylate monomers, such as, optionally and preferably, one or more brominated aromatic (meth)acrylate monomers.
As stated above, the composition of the invention is polymerizable. Polymerization can be accomplished by usual means, such as heating in the presence of a free-radical initiator, irradiation with electromagnetic radiation such as ultraviolet or visible light in the presence of suitable photoinitiators, and by electron beam. For reasons of convenience and production speed, the preferred method of polymerization is by irradiation with ultraviolet or visible light in the presence of photoinitiator. Examples of photoinitiators that are useful in the polymerizable composition include, but are not limited to, those commercially available from Ciba Geigy of Tarrytown, N.Y. under the trade designations Darocur 1173, Darocur 4265, Irgacure 651, Irgacure 1800, Irgacure 369, Irgacure 1700, and Irgacure 184, and Irgacure 907. Photoinitiators containing phosphine oxide derivatives are preferred. A preferred photoinitiator is Lucirin(copyright) TPO, (2,4,6-trimethylbenzoy) diphenyl phosphine oxide, commercially available from BASF of Charlotte N.C. The photoinitiator can preferably be present in amounts in the range from about 0.1-10 parts by weight per 100 parts by weight of polymerizable composition (pph).
The polymerizable composition can also contain one or more other useful ingredients that, as will be appreciated by those skilled in the polymer art, can be useful in such a polymerizable composition. For example, the polymerizable composition might contain a crosslinking agent, one or more surfactants, pigments, fillers, polymerization inhibitors or other ingredients that can be useful within a polymerizable composition or an optical product. Such ingredients can be included in the composition in amounts known to be effective for their respective purposes.
A crosslinking agent can be useful to increase the glass transition temperature of the polymer resulting from crosslinking the polymerizable composition. Glass transition temperature of a composition can be measured by methods known in the art, such as Differential Scanning Calorimetry (DSC), modulated DSC (MDSC), or Dynamic Mechanical Analysis (DMA). Illustrative examples of suitable crosslinking agents include diallyl phthalate, diallyl terephthalate, 1,3,5-tri-(2-(meth)acryloxyethyl)-s-triazine, and crosslinkers that are commercially available as, e.g., EB 220 (UCB-Radcure of Smyrna Ga.), Ebercryl 3603 (Acrylated epoxy novolac from UCB-Radcure), Ebercryl 693, CN112C60 (Sartomer), Ebercryl 6602 (trifunctional aromatic urethane acrylate).
Surfactants such as fluorosurfactants can be included in the polymerizable composition to reduce surface tension, improve wetting, allow smoother coating and fewer defects of the coating, etc. Specific examples of useful surfactants include nonionic fluorosurfactants sold by the 3M Company of St. Paul, Minn. under the trade names FC-430, FC-171, and FC-740. Such surfactants can be included in the polymerizable composition, e.g., in an amount in the range from about 0.01 to 0.3 parts by weight per 100 parts of polymerizable composition.
Polymeric beads, inorganic fillers, and/or pigments can be added to the polymerizable composition in order to improve processing, to impart slip and scratch resistance to the polymerized material, or to affect optical properties of the polymerized material. Examples of useful polymeric beads include those made of polystyrene, polyacrylates, copolymers of styrene and acrylates, polyethylene, polypropylene, polytetrafluoroethylene, or combinations thereof Examples of inorganic fillers and pigments include solid or hollow glass beads, silica, zirconia, aluminum trihydroxide, and titanium dioxide. The mean particle size can be between 1 and 20 micrometer (um), and the particles can be included in the polymerizable composition in an amount in the range from about 0.25 to 7 weight percent, more preferably from about 0.25 to 2 weight percent.
The polymerizable composition can be formed into any of various known and useful high index of refraction, optical products or articles. These articles can be used in numerous applications where it is desired to efficiently control the flow and intensity of light, for example to produce optical lenses, optical films such as high index of refraction films (e.g., those referred to as Brightness Enhancement Films, including multilayer films and films containing one or more microreplicated layers). The production of optical products from high index of refraction, polymerizable materials, is described, for example, in U.S. Pat. Nos. 5,175,030, 5,183,597, and 5,591,527, the disclosures of which are incorporated herein by reference.
The invention will be more fully appreciated with reference to the following non-limiting examples in which the reaction components are given as grams used, or weight percents (wt %) based on the total weight of the polymerizable composition. Dimensions in English units are nominal and conversion to metric units is approximate.